With the progress of miniaturization of semiconductor element, shortening of the wavelength of exposure light source and increasing of the numerical aperture (high NA) of projection lens have advanced, and now an exposure apparatus using an ArF excimer laser having a wavelength of 193 nm as the light source have been developed. In recent years, as a method for achieving the formation of a finer pattern, immersion lithography to which a technique for increasing resolution as to an optical microscope is applied has been known. According to the immersion lithography, the exposure is performed while filling a liquid of high refractive index (hereinafter also referred to as an “immersion liquid”) between a projection lens and a sample.
The recent technical progress of immersion exposure is reported, for example, in SPIE Proc., 4688, 11 (2002), J. Vac. Sci. Technol. B, 17 (1999) and JP-A-10-303114 (the term “JP-A” as used herein means an “unexamined published Japanese patent application”). When an ArF excimer laser is used as the light source, it is believed that pure water (having a refractive index of 1.44 at 193 nm) is most promising as the immersion liquid in view of the safety in handling and the transmittance and refractive index at 193 nm.
In WO 2004/068242 (corresponding to US2005/0014090A1), an example is described wherein the resist performance changes by the immersion of a resist for ArF exposure in water before and after exposure and it is pointed out that this is a problem in the immersion exposure. Also, in JP-A-2006-58842, a problem is pointed out in that a component, for example, an acid, in the resist dissolves from the resist layer in the immersion liquid to cause contamination on the surface of lens.
As a means of solving the problems, it is proposed that the migration (dissolution) of resist component in the immersion liquid during the contact of the resist layer with the immersion liquid in the exposure step can be prevented by adding a substance which moves to the upper portion of the resist layer after coating in JP-A-2006-48029 (corresponding to US2006/0008736A1) and JP-A-2006-309245 (corresponding to US2006/0246373A1).
Further, as a result of intensive investigations, it has been found that the addition of a hydrophobic resin to the resist layer not only can prevent the dissolution of resist component but also can hydrophobilize the surface layer so that a receding contact angle of the surface of resist layer against water can be increased to improve the followability of immersion liquid when the resist layer is brought into contact with water in case of using water as the immersion liquid medium.
However, in case of coating a resist to which a resin including a high molecular weight component is added, a phase separation occurs at the formation of a layer on the surface thereby degrading coating property. Also, since the high molecular weight component is insoluble in alkali, it is necessary to improve development defect.